Lens barrel having a linear guide mechanism

ABSTRACT

A lens barrel is disclosed that includes: an outer barrel provided on an inner periphery thereof with a first thread and at least one linear guide groove intersecting the first thread and extending in a direction of an optical axis of the lens barrel; a middle barrel provided on an outer periphery thereof with a second thread meshing with the first thread; an inner barrel positioned inside the middle barrel, the inner barrel being provided with at least one follower which engages with the at least one linear guide groove, so that the inner barrel is guided along the optical axis without rotating about the optical axis with respect to the outer barrel; and a recess formed at a front end of each of the at least one linear guide groove on the inner periphery of the outer barrel, the recess having a width dimension to enable rotational movement of the at least one follower into the at least one linear guide groove during initial meshing of the middle barrel with the outer barrel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens barrel having a linear guidemechanism for guiding a linear moving barrel, provided in the lensbarrel, along an optical axis thereof, without rotating about theoptical axis.

2. Description of the Related Art

A conventional lens-shutter type of zoom lens camera having atelescoping type of zoom lens barrel, is widely known. In such a type ofzoom lens camera, a zoom lens barrel unit is usually assembledseparately from a main body (camera body) of the camera, before beinginstalled in a housing of the camera body. The housing of the camerabody is usually provided on an inner peripheral surface thereof with afemale helicoid and a plurality of linear guide grooves intersecting thefemale helicoid and extending in the optical axis direction. With thecamera body having such a housing, the zoom lens barrel unit is usuallyinstalled using the following method. Namely, the zoom lens barrel unitis firstly inserted into the housing from a rear of the housing.Subsequently, the male helicoid, formed on an outer peripheral surfaceof the outermost barrel of the zoom lens barrel unit, is brought intomesh with the female helicoid, formed on an inner periphery of thehousing. Thereafter, a linear guide plate, provided with a plurality ofradial follower projections, is secured to the rear end of the outermostbarrel, with the plurality of follower projections engaging with theplurality of linear guide grooves of the housing.

According to such an installing method, it is necessary to carry outseveral processes to install the zoom lens barrel unit in the housing ofthe camera body. This is troublesome, and increases installation time.

When a lens barrel is designed having a guide groove or a cam grooveformed on an inner peripheral surface thereof which engages with afollower projection provided on a predetermined member to guide the samealong the groove, the width and depth of the groove, which areconsidered to be sufficient to maintain the mechanical strength of thelens barrel, are firstly determined before the whole dimension of thelens barrel (thickness, diameter, etc.) is determined. Therefore, ingeneral, such a lens barrel having a guide or cam groove tends to bedesigned as a member which is too thick and too large.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a lens barrel having alinear guide mechanism for guiding a linear moving barrel along anoptical axis, which is space-efficient and simplifies the processnecessary for installing the zoom lens barrel unit in the housing of thecamera.

Another object of the present invention is to provide a lens barrelhaving a linear guide mechanism for guiding a linear moving barrel alongan optical axis, which makes it possible to realize a small-sized lensbarrel, while maintaining a sufficient mechanical strength of the lensbarrel.

To achieve the former object mentioned above, according to an aspect ofthe present invention, there is provided a lens barrel including: anouter barrel provided on an inner periphery thereof with a first threadand at least one linear guide groove intersecting the first thread andextending in a direction of an optical axis of the lens barrel; a middlebarrel provided on an outer periphery thereof with a second threadmeshing with the first thread; an inner barrel positioned inside themiddle barrel, the inner barrel being provided with at least onefollower which engages with the at least one linear guide groove, sothat the inner barrel is guided along the optical axis without rotatingabout the optical axis with respect to the outer barrel; and a recessformed at a front end of each of the at least one linear guide groove onthe inner periphery of the outer barrel, the recess having a widthdimension to enable rotational movement of the at least one followerinto the at least one linear guide groove during initial meshing of themiddle barrel with the outer barrel. With this structure, the recess isused not only for bringing the middle barrel into mesh with the outerbarrel but also for forming part of the linear guide groove. Thus, therecess is space-efficiently formed on a front part of the outer barrel,which contributes to the realization of a small and compact lens barrel.

Preferably, the lens barrel further includes an annular retaining memberwhich engages with a front end of the outer barrel, after the middlebarrel has been engaged with the outer barrel.

Preferably, the annular retaining member is provided with at least oneengaging projection which engages with the at least one recess.

Preferably, the at least one engaging projection has a surfacedetermining a front extremity of the at least one linear guide groove.

According to another aspect of the present invention, there is provideda lens barrel including: an outer barrel provided on an inner peripherythereof with a first thread and a plurality of linear guide grooves eachintersecting the first thread and extending in a direction of an opticalaxis of the lens barrel; a middle barrel provided on an outer peripherythereof with a second thread meshing with the first thread, so that themiddle barrel is movable along the optical axis while rotating about theoptical axis with respect to the outer barrel; an inner barrelpositioned inside the middle barrel and moved together with the innerbarrel along the optical axis, the inner barrel being provided at a rearend thereof with a plurality of followers which respectively engage withthe plurality of linear guide grooves, so that inner barrel is guidedalong the optical axis without rotating about the optical axis withrespect to the outer barrel; a plurality of recesses each formed at afront end of a corresponding one of the plurality of linear guidegrooves on the inner periphery of the outer barrel, the plurality ofrecesses each having a width greater than the corresponding one of theplurality of linear guide grooves; and an annular retaining member forpreventing the middle barrel from disengaging from the outer barrel, theannular retaining member being provided with a plurality of engagingprojections each extending in the direction of the optical axis toengage with a corresponding one of the plurality of recesses, theannular retaining member being secured to a front end of the outerbarrel, after the middle barrel has been engaged with the outer barrel,with the plurality of engaging projections respectively engaged with theplurality of linear guide grooves.

According to yet another aspect of the present invention, there isprovided a lens barrel including: an outer barrel provided on an innerperiphery thereof with a first thread; a middle barrel provided on anouter periphery thereof with a second thread meshing with the firstthread of the outer barrel; an inner barrel positioned inside the middlebarrel and provided with at least one follower; an annular retainingmember secured to a front end of the outer barrel for preventing themiddle barrel from disengaging from the outer barrel; at least onelinear guide groove which extends in a direction of an optical axis ofthe lens barrel and with which the at least one follower engages,wherein a part of the at least one linear guide groove is formed on theannular retaining member and a remaining part of the at least one linearguide groove is formed on an inner periphery of the outer barrel.

To achieve the latter object mentioned above, according to anotheraspect of the present invention, there is provided a lens barrelincluding: a barrel provided on an inner periphery thereof with a linearguide groove extending in a direction of an optical axis of the lensbarrel; and an annular member arranged concentrically with the barrel,the annular member being provided with a follower which engages with thelinear guide groove so that the annular member is guided along theoptical axis without rotating about the optical axis relative to thebarrel, wherein a part of an outer periphery of the barrel which islocated adjacent to the linear guide groove is formed as a planesurface, and further wherein a distance between the plane surface andthe optical axis is shorter than a distance between the optical axis anda part of the outer periphery of the barrel which is not formed as theplane surface.

Preferably, a bottom of the linear guide groove is formed as a planebottom surface extending in the direction of the optical axis andperpendicular to a radial direction of the barrel, the plane surfacebeing formed parallel to the plane bottom surface.

According to yet another aspect of the present invention, there isprovided a lens barrel including: an outer barrel provided on an innerperiphery thereof with a first thread and a linear guide grooveintersecting the first thread and extending in a direction of an opticalaxis of the lens barrel; a middle barrel provided on an outer peripherythereof with a second thread meshing with the first thread; an innerbarrel positioned inside the middle barrel and provided with a followerwhich engages with the linear guide groove to be guided along the linearguide groove, the middle barrel being movable along the optical axistogether with the inner barrel without varying a distance between themiddle and the inner barrels while the middle barrel rotates about theoptical axis relative to the inner barrel; and at least one projectionformed at a bottom of the linear guide groove, the at least oneprojection engaging with the second thread so as to function as a partof the first thread.

According to yet another aspect of the present invention, there isprovided a lens barrel including: a barrel provided on an innerperiphery thereof with a plurality of linear guide grooves eachextending in a direction of an optical axis of the lens barrel; and anannular member arranged concentrically with the barrel, the annularmember being provided with a plurality of followers which respectivelyengage with the plurality of linear guide grooves so that the annularmember is guided along the optical axis without rotating about theoptical axis relative to the barrel, wherein a part of the barrel whereone of the plurality of linear guide grooves is formed has a thicknessthinner than any other parts of the barrel where the rest of theplurality of linear guide grooves are formed.

The present disclosure relates to subject matter contained in JapanesePatent Applications No.8-12317 (filed on Jan. 26, 1996), No.8-21438(filed on Feb. 7, 1996), No.8-34037 (filed on Feb. 21, 1996) andNo.8-184791 (filed on Jul. 15, 1996) which are expressly incorporatedherein by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in detail with reference to theaccompanying drawings in which similar elements are indicated by similarreference numerals, and wherein:

FIG. 1 is a schematic perspective view of a fixed lens barrel block anda zoom lens barrel unit provided in a zoom lens camera, illustrating astate before the zoom lens barrel unit is installed in the fixed lensbarrel block;

FIG. 2 is a schematic perspective view of the fixed lens barrel block,the zoom lens barrel unit and an annular fixing member, illustrating astate after the zoom lens barrel unit is installed in the fixed lensbarrel block;

FIG. 3 is a schematic perspective view of the fixed lens barrel blockshown in FIGS. 1 or 2;

FIG. 4 is an enlarged schematic perspective view of a third movingbarrel shown in FIGS. 1 or 2;

FIG. 5 is an enlarged schematic perspective view of the annular fixingmember shown in FIG. 2;

FIG. 6 is a schematic developed view of a part of the fixed lens barrelblock shown in FIGS. 1, 2 or 3, illustrating a linear guide mechanism ofthe zoom lens barrel unit;

FIG. 7 is a schematic developed view of the part of the fixed lensbarrel block shown in FIG. 6 and a part of the annular fixing memberengaged with the fixed lens barrel block, illustrating the linear guidemechanism in a different state from that shown in FIG. 6;

FIG. 8 is an enlarged view of a part of the view shown in FIG. 7;

FIG. 9 is an enlarged schematic perspective view showing a part of azoom lens barrel;

FIG. 10 is schematic perspective view showing the part of the zoom lensbarrel shown in FIG. 9 in an engaged state;

FIG. 11 is a schematic perspective view illustrating a state where anAF/AE shutter unit of the zoom lens barrel is mounted to a first movingbarrel;

FIG. 12 is an enlarged exploded perspective view of a part of the zoomlens barrel;

FIG. 13 is an exploded perspective view illustrating main parts of theAF/AE shutter unit of the zoom lens barrel shown in FIGS. 9, 10, 11 or12;

FIG. 14 is an enlarged schematic perspective view of the third movingbarrel shown in FIG. 4 shown from a different angle;

FIG. 15 is an enlarged perspective view of a linear guide barrel of thezoom lens barrel;

FIG. 16 is a front elevational view of the fixed lens barrel block shownin FIG. 3 with other members installed in the fixed lens barrel block;

FIG. 17 is a sectional view of an upper part of the zoom lens barrel ina maximum extended state;

FIG. 18 is a sectional view of an upper part of the zoom lens barrel,illustrating essential elements in a housed state;

FIG. 19 is a sectional view of the upper part of the zoom lens barrelshown in FIG. 18 in the maximum extended state;

FIG. 20 is a sectional view of an upper part of the zoom lens barrel inthe housed state;

FIG. 21 is an exploded perspective view of the overall structure of thezoom lens barrel;

FIG. 22 is a block diagram of a controlling system for controlling anoperation of the zoom lens barrel;

FIG. 23 is a rear elevational view of the fixed lens barrel block andsome other members installed in the fixed lens barrel block, shown inFIG. 16;

FIG. 24 is a sectional view of an upper part of the zoom lens barrel;

FIG. 25 is a sectional view of the fixed lens barrel block and thelinear guide barrel 17, showing the state of engagement of engagingprojections and linear guide grooves;

FIG. 26 is a plan view of a part of a cylindrical portion formedintegral with the fixed lens barrel block;

FIG. 27 is a diagram illustrating the difference in thickness of thecylindrical portion between a part of the cylindrical portion where onelinear guide groove is formed and another part of the cylindricalportion where another guide groove, having a wider width, is formed;

FIG. 28 is an enlarged sectional view of an engaging projection and alinear guide groove with which the engaging projection engages;

FIG. 29 is a sectional view of the fixed lens barrel block and a wallforming a film chamber of the zoom lens camera;

FIG. 30 is a sectional view of an upper part of a lens supporting barrelwhich supports a front lens group therein, and a lens fixing ring whichis to be screw-engaged with the lens supporting barrel;

FIG. 31 is an enlarged perspective view of the lens supporting barrelshown in FIG. 30; and

FIG. 32 is an enlarged sectional view of a part of the lens fixing ringshown in FIG. 30.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 22 is a schematic representation of various elements which comprisea preferred embodiment of a zoom lens camera to which the presentinvention is applied. A concept of the present zoom lens camera will nowbe described with reference to FIG. 22.

The zoom lens camera is provided with a zoom lens barrel (zoom lens) 10of a three-stage delivery type (telescoping type) having three movingbarrels, namely a first moving barrel 20, a second moving barrel 19 anda third moving barrel 16, which are concentrically arranged in thisorder from an optical axis O. In the zoom lens barrel 10 two lens groupsare provided as a photographic optical system, namely a front lens groupL1 having positive power and a rear lens group L2 having negative power.

In the camera body, a whole optical unit driving motor controller 60, arear lens group driving motor controller 61, a zoom operating device 62,a focus operating device 63, an object distance measuring apparatus 64,a photometering apparatus 65, and an AE (i.e., automatic exposure) motorcontroller 66, are provided. Although the specific focusing system ofthe object distance measuring apparatus 64, which is used to provideinformation regarding the object-to-camera distance, does not form partof the present invention, one such suitable system is disclosed incommonly assigned U.S. patent application Ser. No. 08/605,759, filed onFeb. 22, 1996, the entire disclosure of which is expressly incorporatedby reference herein. Although the focusing systems disclosed in U.S.patent application Ser. No. 08/605,759 are of the so-called "passive"type, other known autofocus systems (e.g., active range finding systemssuch as those based on infrared light and triangulation) may be used.Similarly, a photometering system as disclosed in the above-noted U.S.patent application Ser. No. 08/605,759 could be implemented asphotometering apparatus 65.

The zoom operating device 62 can be provided in the form of, forexample, a manually-operable zoom operating lever (not shown) providedon the camera body or a pair of zoom buttons, e.g., a "wide" zoom buttonand a "tele" zoom button, (not shown) provided on the camera body. Whenthe zoom operating device 62 is operated, the whole optical unit drivingmotor controller 60 drives a whole optical unit driving motor 25 to movethe front lens group L1 and the rear lens group L2, rearwardly orforwardly without regard to a focal length and a focal point thereof. Inthe following explanation, forward and rearward movements of the lensgroups L1 and L2 by the whole optical unit driving motor controller 60(the motor 25) are referred to as the movement toward "tele" and themovement toward "wide" respectively, since forward and rearwardmovements of the lens groups L1 and L2 occur when the zoom operatingdevice 62 is operated to "tele" and "wide" positions.

The image magnification of the visual field of a zoom finder 67 providedin the camera body varies in sequence with the variation of the focallength through the operation of the zoom operating device 62. Therefore,the photographer can perceive the variation of the focal length byobserving the variation of image magnification of the visual field ofthe finder. In addition, the focal length, set by the operation of thezoom operating device 62, may be perceived by a value indicated on anLCD (liquid crystal display) panel (not shown) or the like.

When the focus operating device 63 is operated, the whole optical unitdriving motor controller 60 drives the whole optical unit driving motor25. At the same time the rear lens group driving motor controller 61drives a rear lens group driving motor 30. Due to the driving of thewhole optical unit driving motor controller 60 and the rear lens groupdriving motor controller 61, the front and rear lens groups L1 and L2are moved to respective positions corresponding to a set focal lengthand a detected object distance and thereby the zoom lens is focused onthe subject.

Specifically, the focus operating device 63 is provided with a releasebutton (not shown) provided on an upper wall of the camera body. Aphotometering switch and a release switch (both not shown) aresynchronized with the release button. When the release button ishalf-depressed (half step), the focus operating device 63 causes thephotometering switch to be turned ON, and the object distance measuringand photometering commands are respectively input to the object distancemeasuring apparatus 64 and the photometering apparatus 65.

When the release button is fully depressed (full step), the focusoperating device 63 causes the release switch to be turned ON, andaccording to the result of object distance measuring demand and a setfocal length, the whole optical unit driving motor 25 and the rear lensgroup driving motor 30 are driven, and the focusing operation, in whichthe front lens group L1 and the rear lens group L2 move to the focusingposition, is executed. Further, an AE motor 29 of an AF/AE (i.e.,autofocus/autoexposure) shutter unit (electrical unit) 21 (FIG. 20) isdriven via the AE motor controller 66 to actuate a shutter 27. Duringthe shutter action, the AE motor controller 66 drives the AE motor 29 toopen shutter blades 27a of the shutter 27 for a specified period of timeaccording to the photometering information output from the photometeringapparatus 65.

When the zoom operating device 62 is operated, the zoom operating device62 drives the whole optical unit driving motor 25 to move the front andrear lens groups L1 and L2 together as a whole in the direction of theoptical axis O (optical axis direction). Simultaneous with such amovement, the rear lens group driving motor 30 may also be driven viathe rear lens group driving motor controller 61 to move the rear lensgroup L2 relative to the front lens group L1. However, this is notperformed under the conventional concept of zooming in which the focallength is varied sequentially without moving the position of the focalpoint. When the zoom operating device 62 is operated, the following twomodes are available, namely:

1. a mode to move the front lens group L1 and the rear lens group L2 inthe optical axis direction without varying the distance therebetween bydriving only the whole optical unit driving motor 25; and,

2. a mode to move the front lens group L1 and the rear lens group L2 inthe optical axis direction while varying the distance therebetween bydriving both the whole optical unit driving motor 25 and the rear lensgroup driving motor 30.

In mode 1, during a zooming operation an in-focus condition cannot beobtained at all times with respect to a subject located at a specificdistance. However, this is not a problem in a lens-shutter type camera,since the image of the subject is not observed through the photographingoptical system, but through the finder optical system that is providedseparate from the photographing optical system, and it is sufficient toonly be focused when the shutter is released. In mode 2, during azooming operation, the front lens group L1 and the rear lens group L2are moved without regard to whether the focal point moves, and when theshutter is released, the focusing operation (focus adjusting operation)is carried out by moving both the whole optical unit driving motor 25and the rear lens group driving motor 30.

When the focus operating device 63 is operated in at least one part ofthe focal length range set by the zoom operating device 62, the wholeoptical unit driving motor 25 and the rear lens group driving motor 30are driven to bring the subject into focus. The amount of movement ofeach lens group L1 or L2 by the whole optical unit driving motor 25 andthe rear lens group driving motor 30 is determined not only usingsubject distance information provided from the object distance measuringapparatus 64, but also by using focal length information set by the zoomoperating device 62. In such a manner, when the focus operating device63 is operated, by moving both the whole optical unit driving motor 25and the rear lens group driving motor 30, the position of the lensgroups L1, L2 can be flexibly controlled, as compared with lensmovements controlled by cam.

The zoom lens camera of this embodiment can also be controlled in adifferent manner such that, during an operation of the zoom operatingdevice 62, only the magnification of the zoom finder 67 and the focallength information are varied without driving either the whole opticalunit driving motor 25 or the rear lens group driving motor 30. When thefocus operating device 63 is operated, both the whole optical unitdriving motor 25 and the rear lens group driving motor 30 are movedsimultaneously according to the focal length information and the subjectdistance information obtained by the object distance measuring apparatus64 to move the front lens group L1 and the rear lens group L2 torespective positions determined according to the focal length and thesubject distance information.

An embodiment of the zoom lens barrel according to the above conceptwill now be described with reference to mainly FIGS. 21 and 22.

The overall structure of the zoom lens barrel 10 will firstly bedescribed.

The zoom lens barrel 10 is provided with the first moving barrel 20, thesecond moving barrel 19, the third moving barrel 16, and a fixed lensbarrel block 12. The third moving barrel 16 is engaged with acylindrical portion 12p of the fixed lens barrel block 12, and moves inthe optical axis direction upon being rotated. The third moving barrel16 is provided on an inner periphery thereof with a linear guide barrel17, which is restricted in rotation. The linear guide barrel 17 and thethird moving barrel 16 move together as a whole in the optical axisdirection, with the third moving barrel 16 rotating relative to thelinear guide barrel 17. The first moving barrel 20 moves in the opticalaxis direction with rotation thereof being restricted. The second movingbarrel 19 moves in the optical axis direction, while rotating relativeto the linear guide barrel 17 and the first moving barrel 20. The wholeoptical unit driving motor 25 is secured to the fixed lens barrel block12. A shutter mounting stage 40 is secured to the first moving barrel20. The AE motor 29 and the rear lens group driving motor 30 are mountedon the shutter mounting stage 40. The front lens group L1 and the rearlens group L2 are respectively supported by a lens supporting barrel(lens supporting annular member) 34 and a lens supporting barrel 50.

An O-ring 70, made of a rubber or the like, is positioned between anouter peripheral circumferential surface of the lens supporting barrel34, in the vicinity of the front end thereof, and an inner peripheralcircumferential surface of an inner flange portion 20b formed integralwith the first moving barrel 20 in the vicinity of the front endthereof, as shown in FIG. 20. The O-ring 70 prevents water frompenetrating the zoom lens barrel 10 at the front end thereof between thefirst moving barrel 20 and the lens supporting barrel 34.

As shown in FIG. 30, the front lens group L1 consists of five lenses,namely, a first lens (frontmost lens) L1a, a second lens L1b, a thirdlens L1c, a fourth lens L1d and a fifth lens L1e in this order from anobject side to an image side, i.e., from the left hand side to the righthand side as viewed in FIG. 30.

A front positioning ring 36 for determining a distance between thesecond lens L1b and the third lens L1c is positioned and held betweenthe second lens L1b and the third lens L1c. An outer peripheral surfaceof the positioning ring 36 is fitted on an inner peripheral surface ofthe lens supporting barrel 34. Likewise, a rear positioning ring 37 fordetermining a distance between the third lens L1c and the fourth lensL1d is positioned and held between the third lens L1c and the fourthlens L1d. An outer peripheral surface of the positioning ring 37 isfitted on an inner peripheral surface of the lens supporting barrel 34.The rear surface of the fourth lens L1d and the front surface of thefifth lens L1e are cemented to each other, so that the fourth and fifthlenses L1d, L1e are formed as a cemented or composite lens. A frontcircumferential edge L1f of the second lens L1b along thecircumferential edge thereof contacts the rear surface of the first lensL1a. A rear circumferential edge L1g of the fifth lens L1e along thecircumferential edge thereof contacts an inwardly-projecting flange 34bformed integral with the rear end of the lens supporting barrel 34.

A female thread 34a is formed on an inner periphery of a front part ofthe lens supporting barrel 34, as shown in FIGS. 30 or 31. A lens fixingring 72, for fixing the first lens L1a to the lens supporting barrel 34,engages with the lens supporting barrel 34. With this arrangement, amale thread 72a formed on the outer peripheral surface of the lensfixing ring 72 meshes with the female thread 34a. A circular abuttingsurface 72b is formed on the lens fixing ring 72 on an inner peripheralsurface thereof. The circular abutting surface 72b comes into contactwith a circumferential portion fp of the front surface of the first lensL1a in a state when the lens fixing ring 72 is properly screw-engagedwith the lens supporting barrel 34. The circular abutting surface 72b isformed to be substantially parallel to the circumferential portion fp sothat the circular abutting surface 72b and the circumferential portionfp may be brought tightly into contact with each other when the lensfixing ring 72 is properly screw-engaged with the lens supporting barrel34.

A supporting ring portion 34c is formed integral with the lenssupporting barrel 34. The supporting ring portion 34c is locatedinwardly from the female thread 34a in a radial direction of the lenssupporting barrel 34. The inner peripheral surface of the supportingring portion 34c, which extends in the optical axis direction, comesinto contact with an outer circumferential edge or surface op of thefirst lens L1a. An annular positioning surface 34d, extendingsubstantially normal to the optical axis O, is formed on the lenssupporting barrel 34 immediately behind the supporting ring portion 34c.The circumferential edge of the rear surface of the first lens L1a comesinto contact with the positioning surface 34d. With this structure, thefirst lens L1a is immovably held between the circular abutting surface72b and the positioning surface 34d in the optical axis direction, andthe first lens L1a is immovably held by the supporting ring portion 34cin a radial direction normal to the optical axis O.

As shown in FIG. 32, a coating 72e is coated on the circular abuttingsurface 72b. The coating 72e is a waterproof coating made of a syntheticresin. In the present embodiment, "Fantas Coat SF-6 (trademark of acoating produced by the Japanese Company "Origin Denki KabushikiKaisha")" is used as the coating 72e. The front surface of the firstlens L1a is formed very smooth, whereas the circular abutting surface72b of the lens fixing ring 72 is not formed as smoothly (i.e., has arough finish) as the front surface of the first lens L1a. This isbecause the first lens L1a is more minutely and accurately formed thanthe lens fixing ring 72 since the first lens L1a is a precision opticalelement. Due to this fact, were it not for the coating 72e on thecircular abutting surface 72b, a substantial gap would be formed betweenthe circular abutting surface 72b and the circumferential portion fpeven if the circular abutting surface 72b properly and tightly incontact with the circumferential portion fp by properly screw-engagingthe lens fixing ring 72 with the female thread 34a. As a result, wateror moisture would be able to penetrate into the lens supporting barrel34 through the substantial gap. However, in the present embodiment, thecoating 72e is applied to the circular abutting surface 72b so as tomake the surface thereof a smooth surface which does not cause to formsuch a substantial gap between the circular abutting surface 72b and thecircumferential portion fp when the circular abutting surface 72bproperly contacts the circumferential portion fp. Accordingly, thecoating 72e, positioned and held between the circular abutting surface72b and the circumferential portion fp, effectively prevents water ormoisture from penetrating the lens supporting barrel 34 between thecircular abutting surface 72b and the circumferential portion fp underthe condition that the circular abutting surface 72b is properly andtightly in contact with the circumferential portion fp by properlyscrew-engaging the lens fixing ring 72 with the female thread 34a.

A circular surface 72c is formed on the lens fixing ring 72. Thecircular surface 72c is connected to the circular abutting surface 72band is located immediately outward in a radial direction from thecircular abutting surface 72b. A front part of the outer circumferentialsurface op of the first lens L1a (i.e., a circumferential edge of thefirst lens L1a) comes into contact with the circular surface 72c whenthe lens fixing ring 72 properly engages with the female thread 34a. Dueto the circular surface 72c contacting the outer circumferential surfaceop, the watertight structure between the circular abutting surface 72band the circumferential portion fp, that is realized by the coating 72e,is enhanced. That is, a highly efficient watertight connection betweenthe first lens L1a and the lens fixing ring 72 is realized by providingboth the coating 72e and the circular surface 72c with the lens fixingring 72.

An annular recessed portion 34e is formed on the lens supporting barrel34 between the female thread 34a and the supporting ring portion 34c. Asshown in FIG. 20, in a state where the lens fixing ring 72 is properlyscrew-engaged with the female thread 34a, a rear end 72d of the lensfixing ring 72 is positioned in the annular recessed portion 34e withthe rear end 72d not contacting the bottom (i.e., rearmost end) of therecessed portion 34e, namely, an annular space is formed in the annularrecessed portion 34e between the rear end 72d and the bottom of therecessed portion 34e.

The fixed lens barrel block 12 is fixed in front of an aperture plate 14fixed to the camera body. The aperture plate 14 is provided on a centerthereof with a rectangular-shaped aperture 14a which forms the limits ofeach frame exposed. The fixed lens barrel block 12 is provided, on aninner periphery of the cylindrical portion 12p, with a female helicoid12a, and also a plurality of linear guide grooves 12b each extendingparallel to the optical axis O, i.e., extending in the optical axisdirection. At the bottom of one of the linear guide grooves 12b, namely12b', a code plate 13a, having a predetermined code pattern, is fixed.The code plate 13a extends in the optical axis direction and extendsalong substantially the whole of the length of the fixed lens barrelblock 12. The code plate 13a is part of a flexible printed circuit board13 positioned outside the fixed lens barrel block 12.

In the fixed lens barrel block 12, a gear housing 12c, which is recessedoutwardly from an inner periphery of the cylindrical portion 12p of thefixed lens barrel block 12 in a radial direction while extending in theoptical axis direction, is provided as shown in FIGS. 1, 3, 16 or 21. Inthe gear housing 12c, a driving pinion 15, extending in the optical axisdirection, is rotatably held. Both ends of an axial shaft 7 of thedriving pinion 15 are rotatively supported by a supporting hollow 4,provided in the fixed lens barrel block 12, and a supporting hollow 31a,provided on a gear supporting plate 31 fixed on the fixed lens barrelblock 12 by set screws (not shown), respectively. Part of the teeth ofthe driving pinion 15 project inwardly from the inner periphery of thecylindrical portion 12p of the fixed lens barrel block 12 so that thedriving pinion 15 meshes with an outer peripheral gear 16b of the thirdmoving barrel 16, as shown in FIG. 16.

The fixed lens barrel block 12 is provided on one side thereof (the leftside as viewed in FIG. 1) with a supporting member 32 formed integraltherewith. The whole optical unit driving motor 25 is secured to therear of the supporting member 32. A gear train 26 consisting of aplurality of gears, is accommodated to be supported in the supportingmember 32 on the front thereof. The fixed lens barrel block 12 isfurther provided on the other side thereof (opposite to the side havingthe supporting member 32) with a stationary plate 12m formed integraltherewith. A plurality of projections 12n are integrally formed on thefront of the stationary plate 12m, projecting towards the object side inthe optical axis direction. The fixed lens barrel block 12 is furtherprovided, between the stationary plate 12m and the cylindrical portion12p, with a cutout portion 12k extending in the optical axis direction.The cutout portion 12k is formed by cutting out a part of thecylindrical portion 12p. One end of a flexible printed circuit board 6is fixed and supported on the front of the stationary plate 12m by theprojections 12n, with an intermediate part of the flexible printedcircuit board 6 being laid along the cutout portion 12k. The other endof the flexible printed circuit board 6 is secured to the AF/AE shutterunit 21, as shown in FIG. 11.

On an inner periphery of the third moving barrel 16, a plurality oflinear guide grooves 16c, each extending parallel to the optical axis O,are formed. At an outer periphery of the rear end of the third movingbarrel 16, a male helicoid 16a and the aforementioned outer peripheralgear 16b are provided as shown in FIG. 14. The male helicoid 16a engageswith the female helicoid 12a of the fixed lens barrel block 12. Theouter peripheral gear 16b engages with the driving pinion 15. Thedriving pinion 15 has an axial length sufficient to be capable ofengaging with the outer peripheral gear 16b throughout the entire rangeof movement of the third moving barrel 16 in the optical axis direction.

As shown in FIG. 15, the linear guide barrel 17 is provided, on a rearpart of an outer periphery thereof, with a rear end flange 17d. The rearend flange 17d has a plurality of engaging projections 17c eachprojecting away from the optical axis O in a radial direction. Thelinear guide barrel 17 is further provided, in front of the rear endflange 17d, with a retaining flange 17e. A circumferential groove 17g isformed between the rear end flange 17d and the retaining flange 17e. Theretaining flange 17e has a radius smaller than the rear end flange 17d.The retaining flange 17e is provided with a plurality of cutout portions17f. Each of the cutout portions 17f allows a corresponding engagingprojection 16d to be inserted into the circumferential groove 17g, asshown in FIG. 20.

The third moving barrel 16 is provided, on an inner periphery of therear end thereof, with a plurality of engaging projections 16d. Each ofthe engaging projections 16d projects towards the optical axis O in aradial direction. By inserting the engaging projections 16d into thecircumferential groove 17g, through the corresponding cutout portions17f, the engaging projections 16d are positioned in the circumferentialgroove 17g between the flanges 17d and 17e (see FIG. 20). By rotatingthe third moving barrel 16 relative to the linear guide barrel 17, theengaging projections 16d are engaged with the linear guide barrel 17.

On the rear end of the linear guide barrel 17, an aperture plate 23having a rectangular-shaped aperture 23a approximately the same shape asthe aperture 14a, is fixed.

The relative rotation of the linear guide barrel 17, with respect to thefixed lens barrel block 12, is restricted by the slidable engagement ofthe plurality of engaging projections 17c with the corresponding linearguide grooves 12b, formed parallel to the optical axis O.

A contacting terminal 9 is fixed to one of the engaging projections 17c,namely 17c'. The contacting terminal 9 is in slidable contact with thecode plate 13a, fixed to the bottom of the linear guide groove 12b', togenerate signals corresponding to focal length information duringzooming.

On the inner periphery of the linear guide barrel 17 a plurality oflinear guide grooves 17a are formed, each extending parallel to theoptical axis O. A plurality of lead slots 17b are also formed on thelinear guide barrel 17 as shown in FIGS. 15 or 21. The lead slots 17bare each formed oblique (inclined) to the optical axis O.

The second moving barrel 19 engages with the inner periphery of thelinear guide barrel 17. On the inner periphery of the second movingbarrel 19, a plurality of lead grooves 19c are provided in a directioninclined oppositely to the lead slots 17b. On the outer periphery of therear end of the second moving barrel 19 a plurality of followerprojections 19a are provided. Each of the follower projections 19a has atrapezoidal cross-sectional shape projecting away from the optical axisO in a radial direction. Follower pins 18 are positioned in the followerprojections 19a. Each follower pin 18 consists of a ring member 18a, anda center fixing screw 18b which supports the ring member 18a on thecorresponding follower projection 19a. The follower projections 19a arein slidable engagement with the leading slots 17b of the linear guidebarrel 17, and the follower pins 18 are in slidable engagement with thelinear guide grooves 16c of the third moving barrel 16. With such anarrangement, when the third moving barrel 16 rotates, the second movingbarrel 19 moves linearly in the optical axis direction, while rotating.

On the inner periphery of the second moving barrel 19, the first movingbarrel 20 is engaged. The first moving barrel 20 is provided on an outerperiphery of the rear thereof with a plurality of follower pins 24 eachengaging with the corresponding inner lead groove 19c, and at the sametime the first moving barrel 20 is guided linearly by a linear guidemember 22. The first moving barrel 20 is provided at the front endthereof with a decorative plate 41 secured thereto.

As shown in FIGS. 9 and 10, the linear guide member 22 is provided withan annular member 22a, a pair of guide legs 22b and a plurality ofengaging projections 28. The pair of guide legs 22b project from theannular member 22a in the optical axis direction. The plurality ofengaging projections 28 each project from the annular member 22a awayfrom the optical axis O in a radial direction. The engaging projections28 slidably engage with the linear guide grooves 17a. The guide legs 22bare respectively inserted into linear guides 40c between the innerperipheral surface of the first moving barrel 20 and the AF/AE shutterunit 21.

The annular member 22a of the linear guide member 22 is connected to therear of the second moving barrel 19, such that the linear guide member22 and the second moving barrel 19 are capable of moving along theoptical axis O as a whole, and in addition are capable of relativelyrotating around the optical axis O. The linear guide member 22 isfurther provided on the outer periphery of the rear end thereof with arear end flange 22d. The linear guide member 22 is further provided, infront of the rear end flange 22d, with a retaining flange 22c. Acircumferential groove 22f is formed between the rear end flange 22d andthe retaining flange 22c. The retaining flange 22c has a radius smallerthan the rear end flange 22d. The retaining flange 22c is provided witha plurality of cutout portions 22e, as shown in FIGS. 9 or 10, eachallowing a corresponding engaging projection 19b to be inserted into thecircumferential groove 22f, as shown in FIG. 20.

The second moving barrel 19 is provided on an inner periphery of therear end thereof with a plurality of engaging projections 19b, eachprojecting towards the optical axis O in a radial direction. Byinserting the engaging projections 19b into the circumferential groove22f through the corresponding cutout portions 22e, the engagingprojections 19b are positioned in the circumferential groove 22f betweenthe flanges 22c and 22d. By rotating the second moving barrel 19relative to the linear guide member 22, the engaging projections 19b areengaged with the linear guide member 22. With the above structure, whenthe second moving barrel 19 rotates in the forward or reverse rotationaldirection, the first moving barrel 20 moves linearly, forwardly orrearwardly along the optical axis O, but is restricted from rotating.

At the front of the first moving barrel 20, a barrier apparatus 35having barrier blades 48a and 48b is mounted On an inner peripheral faceof the first moving barrel 20 the AF/AE shutter unit 21 having theshutter 27, consisting of three shutter blades 27a, is engaged andfixed, as shown in FIG. 18. The AF/AE shutter unit 21 is provided with aplurality of fixing holes 40a formed at even angular intervals on theouter periphery of the shutter mounting stage 40. Only one of the fixingholes 40a appears in each of FIGS. 9 through 13.

The aforementioned plurality of follower pins 24, which engage with theinner lead grooves 19c, also serve as a device for fixing the AF/AEshutter unit 21 to the first moving barrel 20. The follower pins 24 areinserted in holes 20a, formed on the first moving barrel 20, and fixedin the fixing holes 40a. With this arrangement the AF/AE shutter unit 21is secured to the first moving barrel 20 as shown in FIG. 11. In FIG. 11the first moving barrel 20 is indicated by phantom lines. The followerpins 24 may be fixed by an adhesive, or the pins 24 may be formed asscrews to be screwed into the fixing holes 40a.

As illustrated in FIGS. 13 and 21, the AF/AE shutter unit 21 is providedwith the shutter mounting stage 40, a shutter blade supporting ring 46fixed on the rear of the shutter mounting stage 40 so as to be locatedinside the shutter mounting stage 40, and the lens supporting barrel 50supported in a state of being capable of movement relative to theshutter mounting stage 40. On the shutter mounting stage 40, the lenssupporting barrel 34, the AE motor 29, and the rear lens group drivingmotor 30, are supported. The shutter mounting stage 40 is provided withan annular member 40f having a circular aperture 40d. The shuttermounting stage 40 is also provided with three legs 40b which projectrearward from the annular member 40f. Three slits are defined betweenthe three legs 40b. Two of the slits comprise the aforementioned linearguides 40c, which slidably engage with the respective pair of guide legs22b of the linear guide member 22 so as to guide the movement of thelinear guide member 22.

The shutter mounting stage 40 supports an AE gear train 45, whichtransmits a rotation of the AE motor 29 to the shutter 27, a lensdriving gear train 42, which transmits rotation of the rear lens groupdriving motor 30 to a screw shaft 43, photointerrupters 56 and 57,connected to a flexible printed circuit board 6, and rotating disks 58and 59, having a plurality of radially formed slits provided in thecircumferential direction. An encoder for detecting whether the rearlens group driving motor 30 is rotating and for detecting an amount ofrotation of the rear lens group driving motor 30 consists of thephotointerrupter 57 and the rotating disk 59. An AE motor encoder fordetecting whether the AE motor 29 is rotating and for detecting anamount of rotation of the AE motor 29 consists of the photointerrupter56 and the rotating disk 58.

The shutter 27, a supporting member 47 which pivotally supports thethree shutter blades 27a of the shutter 27, and a circular drivingmember 49, which gives rotative power to the shutter blades 27a, arepositioned between the shutter mounting stage 40 and the shutter bladesupporting ring 46, secured to the shutter mounting stage 40. Thecircular driving member 49 is provided with three operating projections49a at even angular intervals, which respectively engage with each ofthe three shutter blades 27a. As shown in FIG. 13, the shutter bladesupporting ring 46 is provided at a front end thereof with a circularaperture 46a and with three supporting holes 46b positioned at evenangular intervals around the circular aperture 46a. Two deflectionrestricting surfaces 46c are formed on the outer periphery of theshutter blade supporting ring 46. Each deflection restricting surface46c is exposed outwardly from the corresponding linear guide 40c andslidably supports the inner peripheral face of the corresponding guideleg 22b.

The supporting member 47, positioned in front of the shutter bladesupporting ring 46, is provided with a circular aperture 47a, alignedwith the circular aperture 46a of the shutter blade supporting ring 46,and with three pivotal shafts 47b (only one of which is illustrated inFIG. 13) at respective positions opposite the three supporting holes46b. Each shutter blade 27a is provided at one end thereof with a hole27b into which the corresponding pivotal shaft 47b is inserted, so thateach shutter blade 27a is rotatable about the corresponding pivotalshaft 47b. The major part of each shutter blade 27a, that extends normalto the optical axis O from the pivoted end, is formed as a lightinterceptive portion. All three light interceptive portions of theshutter blades 27a together prevent ambient light, which enters thefront lens group L1, from entering the circular apertures 46a and 47awhen the shutter blades 27a are closed. Each shutter blade 27a isfurther provided, between the hole 27b and the light interceptiveportion thereof, with a slot 27c, through which the correspondingoperating projection 49a is inserted. The supporting member 47 is fixedto the shutter blade supporting ring 46 in such a manner that each shaft47b, which supports the corresponding shutter blade 27a, is engaged withthe corresponding supporting hole 46b of the shutter blade supportingring 46.

A gear portion 49b is formed on a part of the outer periphery of thecircular driving member 49. The gear portion 49b meshes with one of theplurality of gears in the gear train 45 to receive the rotation from thegear train 45. The supporting member 47 is provided, at respectivepositions close to the three pivotal shafts 47b, with three arc grooves47c each arched along a circumferential direction. The three operatingprojections 49a of the circular driving ring 49 engage with the slots27c of the respective shutter blades 27a through the respective arcgrooves 47c. The shutter blade supporting ring 46 is inserted from therear of the shutter mounting stage 40, to support the circular drivingring 49, the supporting member 47 and the shutter 27, and is fixed onthe shutter mounting stage 40 by set screws 90 respectively insertedthrough holes 46x provided on the shutter blade supporting ring 46.

Behind the shutter blade supporting ring 46, the lens supporting barrel50, supported to be able to move relative to the shutter mounting stage40 via guide shafts 51 and 52, is positioned. The shutter mounting stage40 and the lens supporting barrel 50 are biased in opposite directionsaway from each other by a coil spring 3 fitted on the guide shaft 51,and therefore play between the shutter mounting stage 40 and the lenssupporting barrel 50 is reduced. In addition, a driving gear 42a,provided as one of the gears in the gear train 42, is provided with afemale thread hole (not shown) at the axial center thereof and isrestricted to move in the axial direction. The screw shaft 43, one endof which is fixed to the lens supporting barrel 50, engages with thefemale thread hole. Accordingly, the driving gear 42a and the screwshaft 43 together constitute a feed screw mechanism. In such a manner,when the driving gear 42a rotates forwardly or reversely due to drivingby the rear lens group driving motor 30, the screw shaft 43 respectivelymoves forwardly or rearwardly with respect to the driving gear 42a, andtherefore the lens supporting barrel 50, which supports the rear lensgroup L2, moves relative to the front lens group L1.

A holding member 53 is fixed at the front of the shutter mounting stage40. The holding member 53 holds the motors 29 and 30 between the holdingmember 53 and the shutter mounting stage 40. The holding member 53 has ametal holding plate 55 fixed at the front thereof by set screws 99. Themotors 29, 30 and the photointerrupters 56, 57 are connected to theflexible printed circuit board 6. One end of the flexible printedcircuit board 6 is fixed to the shutter mounting stage 40.

After the first, second and third moving barrels 20, 19 and 16, and theAF/AE shutter unit 21 and the like are assembled, the aperture plate 23is fixed to the rear of the linear guide barrel 17, and an annularretaining member 33 is fixed at the front of the fixed lens barrel block12.

During an assembly of the zoom lens camera of the present embodiment, azoom lens barrel unit 100, which consists of the first, second and thirdmoving barrels 16, 19 and 20, the AF/AE shutter unit 21, the front andrear lens groups L1, L2, etc., is assembled, in advance, as a separateunit from the fixed lens barrel block 12. Thereafter, the zoom lensbarrel unit 100 is installed in a housing of the fixed lens barrel block12, i.e., in the cylindrical portion 12p, as shown in FIGS. 1 or 2.

With the zoom lens camera of the present embodiment a differentinstalling method is used than in the case of a conventional zoom lenscamera which is less troublesome and reduces the time necessary forinstalling the zoom lens barrel unit in the housing. In order to utilizethe improved installing method, in the zoom lens barrel 10 a new type oflinear guide mechanism has been realized, which is unique to the zoomlens camera of the present embodiment, for guiding the linear guidebarrel 17 along the optical axis O without having the linear guidebarrel 17 rotate.

With the linear guide mechanism of the present embodiment, no dedicatedspace is necessary which is used only for the purpose of installing ordetaching the zoom lens barrel unit 100 in or from the cylindricalportion 12p. Thus, the size of the zoom lens barrel unit 100 can bereduced thereby contributing to the realization of a compact zoom lenscamera. Such a linear guide mechanism will be discussed with referenceto FIGS. 1 through 8.

The basic process of such an installing method in the zoom lens cameraof the present embodiment will now be discussed. Firstly, as shown inFIG. 1, the zoom lens barrel unit 100 is prepared in its most extendedstate. Secondly while maintaining such a state, the rear end of the zoomlens barrel unit 100 is brought into engagement with the front end ofthe cylindrical portion 12p in a predetermined positional relationship,as shown in FIG. 2. Thereafter, the whole optical unit driving motor 25is driven to rotate the drive pinion 15 (see, for example, FIG. 21) in apredetermined rotational direction, so that the male helicoid 16a of thethird moving barrel 16 engages with the female helicoid 12a.

Since the third moving barrel 16 and the cylindrical portion 12p areengaged with each other through the male and female helicoids 16a, 12a,i.e., through a threaded engagement when the third moving barrel 16 isbrought into engagement with the cylindrical portion 12p, it isnecessary for the third moving barrel 16 to be rotated, from apredetermined initial position of engagement to an engagement completionposition (i.e., the front extremity of the actual movable range of thethird moving barrel 16 for zooming relative to the cylindrical portion12p), about the optical axis O relative to the cylindrical portion 12pby a predetermined rotational amount. Namely, since the male helicoid16a and the outer peripheral gear 16b are formed on the third movingbarrel 16 along a common outer circumferential surface at the rear endof the third moving barrel 16 as shown in FIG. 14, the male and femalehelicoids 16a and 12a can only engage with each other after the thirdmoving barrel 16 has been located at a predetermined rotational positionrelative to the female helicoid 12a. Furthermore, the plurality ofengaging projections 17c, which respectively engage with the pluralityof linear guide grooves 12b, need to be at respective predeterminedrotational positions with respect to the third moving barrel 16 when thethird moving barrel 16 is brought into engagement with the fixed lensbarrel block 12. Thus the third moving barrel 16 needs to be firstlyengaged with the cylindrical portion 12p and subsequently moved to theaforementioned engagement completion position while maintaining theaforementioned predetermined rotational positions of the plurality ofengaging projections 17c, with respect to the third moving barrel 16.

Due to such a structure, in order to set the zoom lens barrel unit 100on the fixed lens barrel block 12 at the aforementioned engagementcompletion position, while maintaining the aforementioned predeterminedrotational positions of the plurality of engaging projections 17c withrespect to the third moving barrel 16, it is necessary to provide adevice for allowing the plurality of engaging projections 17c to move torespective initial positions at which the plurality of engagingprojections 17c start engaging with the linear guide grooves 12b,without allowing the plurality of engaging projections 17c to contactanything, i.e., not being interfered by anything, until the femalehelicoids 12a have been brought to the aforementioned engagementcompletion position. In the linear guide mechanism of the presentembodiment, such a device is provided on the fixed lens barrel block 12,rather than on the zoom lens barrel unit 100. Contrary to the presentembodiment, if such a device is provided on the zoom lens barrel unit100, the device needs to be constructed so as to allow the plurality ofengaging projections 17c to further rotate about the optical axis Orelative to the third moving barrel 16 beyond the actual rotatable rangeused in an actual zooming operation. Namely, in such a device it isnecessary to provide a structure that allows the third moving barrel 16and the linear guide barrel 17 to further rotate relative to each otherto some extent beyond the actual rotatable range used in an actualzooming operation. That is, the device requires that the lead grooves17b, 19c be formed sufficiently long so as to allow the third movingbarrel 16 and the linear guide barrel 17 to further rotate relative toeach other, which renders the zoom lens barrel 10 to be longer andlarger.

Note that in FIGS. 1 and 2 the drive pinion 15, which is accommodated inthe gear housing 12c, is not illustrated, and the gear train 26, whichis supported on the supporting member 32, is not illustrated.

The aforementioned device provided on the fixed lens barrel block 12 isconstructed as follows. As shown in FIGS. 1, 3 or 6, three recessedportions 12g (only one of which is shown in FIGS. 1, 3 or 6), eachrecessed outwardly in a radial direction, are formed on the innerperiphery of the cylindrical portion 12p at the front end thereof suchthat each recessed portion 12g connects with a corresponding one of thelinear guide grooves 12b. Each recessed portion 12g includes a beveledsurface or edge 12e. The beveled surface 12e is inclined in the opticalaxis direction and extends parallel to the female helicoid 12a. Thebeveled surface 12e connects with one of the side surfaces or edges "A"of the corresponding linear guide groove 12b. The other side surface "B"of the linear guide groove 12b extends in the optical axis direction.The front end of the side surface "B" extends to the front end of thecylindrical portion 12p. A front edge 12f of each recessed portion 12gis recessed by a small amount rearwardly from the front end of thecylindrical portion 12p. A cutout portion 12d is formed on the front endof the cylindrical portion 12p at each position on the front edge 12f. Arectangular hole 12h is formed in approximately the middle part of eachrecessed portion 12g thereof.

The annular retaining member 33 (see, for example, FIG. 2) is secured tothe front end of the cylindrical portion 12p at least after the thirdmoving barrel 16 has been engaged with the cylindrical portion 12p witheach of the engaging projections 17c engaging with the correspondinglinear guide groove 12b. Namely, the annular retaining member 33 isbought into engagement with the front end of the cylindrical portion 12pafter the zoom lens barrel unit 100 has been properly installed in thecylindrical portion 12p.

As shown in FIGS. 2, 5 or 7, three engaging projections 33a, which mayrespectively engage with the recessed portions 12g, are integrallyformed on the annular retaining member 33. The annular retaining member33 is secured to the front end of the cylindrical portion 12p throughthe engaging projections 33a.

In addition to the engaging projections 33a, the annular retainingmember 33 is also provided with an annular base 33i. Each of theengaging projections 33a extends rearwardly in the optical axisdirection from the annular base 33i so as to correspond to therespective recessed portions 12g. The annular retaining member 33 isfurther provided with a strip-shaped plate 33g which is integrallyformed on the annular base 33i. The plate 33g extends in the opticalaxis direction at the location corresponding to the position of theaforementioned cutout portion 12k. When the annular retaining member 33properly engages with the cylindrical portion 12p, the plate 33g liesalong or covers the cutout portion 12k so as to prohibit the annularretaining member 33 from rotating about the optical axis O relative tothe cylindrical portion 12p while restricting the movement of theaforementioned intermediate part of the flexible printed circuit board6.

Each engaging projection 33a is provided with a beveled surface 33b, alinear guide surface 33c and a parallel surface 33d. When the annularretaining member 33 properly engages with the cylindrical portion 12p,each beveled surface 33b tightly contacts the corresponding beveledsurface 12e. Additionally, each linear guide surface 33c and the sidesurface "A" of the corresponding linear guide groove 12b are connectedwith each other. Thus, the linear guide surface 33c and the side surface"A" together guide a side edge "C" of the corresponding engagingprojection 17c in the optical axis direction. When the annular retainingmember 33 properly engages with the cylindrical portion 12p, theparallel surface 33d extends parallel to the other side surface "B" ofthe corresponding linear guide groove 12b.

Each engaging projection 33a is further provided with a stop surface 33fwhich extends perpendicular to both the corresponding parallel surface33d and linear guide surface 33c to connect the parallel surface 33dwith the linear guide surface 33c. When the annular retaining member 33properly engages with the cylindrical portion 12p, each stop surface 33fdefines the front end of the corresponding linear guide groove 12b, asshown in FIG. 7.

Specifically, in the state where the annular retaining member 33properly engages with the cylindrical portion 12p, each linear guidesurface 33c and the side surface "A" of the corresponding linear guidegroove 12b are not located in a common plane extending in the opticalaxis direction, but each linear guide surface 33c is slightly recessedaway from the corresponding side surface "B" relative to thecorresponding side surface "A" in a circumferential direction of thecylindrical portion 12p by an amount "a", as shown in FIGS. 7 or 8. Inother words, the linear guide surface 33c is slightly recessed away froman imaginary surface "A'" that is located in a common plane in which theside surface "A" of the corresponding linear guide groove 12b islocated. Therefore, the width of each linear guide groove 12b isslightly wider at the front end thereof, where the linear guide surface33c is provided, than the width of the remaining part of the linearguide groove 12b. The reason why the linear guide surface 33c isrecessed in such a manner will be hereinafter discussed.

Each engaging projection 17c of the linear guide barrel 17 movesforwardly while pressing against the side surface "A" of thecorresponding linear guide groove 12b when the zoom lens barrel 10 isdriven to advance. For this reason, if any of the linear guide surfaces33c are formed closer to the corresponding side surface "B" than theside surface "A" of the corresponding linear guide groove 12b beyond thecorresponding imaginary surface "A'" due to an error in a moldingprocess of the annular retaining member 33 or the like, the engagingprojection 17c, that engages with the linear guide groove 12b includingsuch a linear guide surface 33c, cannot smoothly shift from the sidesurface "A" to the adjacent linear guide surfaces 33c. In order toprevent the occurrence of such a problem, each linear guide surface 33cis formed in such a manner as noted above, i.e., recessed by the amount"a". Owing to such a structure, even if any linear guide surface 33cshould be formed slightly closer to the corresponding side surface "B"due to a manufacturing error, since each linear guide surface 33c isalready made such as to be slightly recessed away from the correspondingside surface "B", the aforementioned problem does not occur. Althougheach linear guide surface 33c and the side surface "A" of thecorresponding linear guide groove 12b are not located in a common planeextending in the optical axis direction, a problem similar to theaforementioned problem does not occur when the zoom lens barrel 10 isdriven to retract back to the camera body.

This is because each engaging projection 17c of the linear guide barrel17 moves rearwardly while pressing against the side surface "B" of thecorresponding linear guide groove 12b when the zoom lens barrel 10 isdriven to retract.

An engaging claw 33h is integrally formed on an outer surface of eachengaging projection 33a. The engaging claws 33h respectively snap intothe rectangular holes 12h when the annular retaining member 33 properlyengages with the cylindrical portion 12p. An engaging projection 33e,which extends rearward from the annular base 33i in the optical axisdirection, is formed on the annular retaining member 33 at a position onan outer surface of each engaging projection 33a. The engagingprojections 33e respectively engage with the cutout portions 12d whenthe annular retaining member 33 properly engages with the cylindricalportion 12p.

According to the linear guide mechanism having the structures as notedabove, the zoom lens barrel unit 100 can be installed in the cylindricalportion 12p in the following manner. Firstly, after the zoom lens barrelunit 100 has been assembled, the zoom lens barrel unit 100, rendered inits most extended state, is prepared. Secondly, while being in such astate, the rear end of the zoom lens barrel unit 100 is fitted in thefront end of the inner periphery of the cylindrical portion 12p with apredetermined positional relationship. That is, the angular position ofthe zoom lens barrel unit 100 relative to the cylindrical portion 12p ispredetermined when the rear end of the zoom lens barrel unit 100 engageswith the front end of the inner periphery of the cylindrical portion12p. Thereafter, the whole optical unit driving motor 25 is actuated torotate the drive pinion 15 by several degrees in a direction to retractthe third moving barrel 16 into the cylindrical portion 12p. Therotation of the whole optical unit driving motor 25 is transmitted tothe third moving barrel 16 through the gear train 26, the drive pinion15 and the outer peripheral gear 16b, thus making the male helicoid 16arotate relative to the female helicoid 12a to thereby retract the thirdmoving barrel 16 to the front extremity of the actual movable range ofthe third moving barrel 16 for zooming. During the retraction movementof the third moving barrel 16 up to the front extremity, the linearguide barrel 17 remains located at a specific rotational position withrespect to the third moving barrel 16, since the zoom lens barrel unit100 is in its most extended state, and because during the retractionmovement of the third moving barrel 16, each engaging projection 17cpasses through the corresponding recessed portion 12g to engage with thecorresponding linear guide grooves 12b, as shown by phantom lines inFIG. 6.

After the third moving barrel 16 has been retracted to the frontextremity of the actual movable range of the third moving barrel 16 forzooming in such a manner as noted above, if the whole optical unitdriving motor 25 is actuated to further rotate the drive pinion 15 in adirection to retract the third moving barrel 16 into the cylindricalportion 12p, the male helicoid 16a rotates relative to the femalehelicoid 12a to thereby retract the third moving barrel 16 into thecylindrical portion 12p. At the same time, the first and second movingbarrels 20, 19 retract into the second and third moving barrels 19, 16,respectively, due to the mechanical structure for driving the first,second and third moving barrels in a predetermined relationship.Consequently, the zoom lens barrel unit 100 moves into its mostretracted state and is accommodated in the cylindrical portion 12p.

According to the linear guide mechanism of the present embodiment forguiding the linear guide barrel 17 along the optical axis O withoutrotating the linear guide barrel 17, the aforementioned device (whichallows the engaging projections 17c to move to respective initialpositions at which the engaging projections 17c start engaging with thelinear guide grooves 12b, without the engaging projections 17ccontacting anything, until the female helicoids 12a have been brought upto the aforementioned engagement completion position) for installing ordetaching the zoom lens barrel unit 100 in or from the fixed lens barrelblock 12 is provided on the fixed lens barrel block 12, not on the zoomlens barrel unit 100, which advantageously does not render the zoom lensbarrel 10 to be longer and larger. Furthermore, the recessed portions12g are used not only for installing or detaching the zoom lens barrelunit 100 in or from the fixed lens barrel block 12 but also for formingpart of the linear guide grooves 12b after the annular retaining member33 has been secured to the front end of the cylindrical portion 12p.Accordingly, it can be understood that the recessed portions 12g arespace-efficiently formed on the front part of the cylindrical portion12p, which contributes to the realization of a small and compact zoomlens barrel 10.

Another feature of the linear guide mechanism of the present embodimentwill be hereinafter discussed mainly with reference to FIGS. 3 and 23through 29.

This feature of the present embodiment concerns one of the plurality oflinear guide grooves 12b, namely the linear guide groove 12bi , and oneof the plurality of engaging projections 17c which engages with thelinear guide groove 12bi, namely the engaging projection 17ci. As shownin FIGS. 23 or 25, the engaging projection 17ci is formed having an"M"-shaped outline so that the engaging projection 17ci does notinterfere with two projections 12a' formed on a bottom of the linearguide groove 12bi. As can be seen from FIGS. 3 or 26, the twoprojections 12a' form part of the female helicoid 12a.

As shown in FIG. 25, another one of the plurality of linear guidegrooves 12b, namely the linear guide groove 12bni, and another one ofthe plurality of engaging projections which engages with the linearguide groove 12bni, namely the engaging projection 17cni, are not formedhaving the aforementioned features of the linear guide groove 12bi andthe engaging projection 17bi.

Strictly speaking, the engaging projection 17ci engages with the linearguide groove 12bi in a manner such that the engaging projection 17ciprojects outwardly from the optical axis O by a length "t'" (amount ofengagement), measured in a radial direction from the root of the femalehelicoid 12a to the tip of the engaging projection 17ci as shown inFIGS. 25 or 28. The tip of the engaging projection 17ci does not contactthe bottom of the linear guide groove 12bi. Reference "w'" shown inFIGS. 25 or 28 represents the width of the engaging projection 17ci.Reference "x1" shown in FIGS. 25 or 28 designates a corner of theengaging projection 17ci. A line connecting "x1" with "x1" (line x1--x1)is identical to the width of the engaging projection 17ci "w'", which issubstantially the same as the width of the linear guide groove 12bi.

On the other hand, the engaging projection 17cniengages with the linearguide groove 12bni in a manner such that the tip portion of the engagingprojection 17cniprojects into the linear guide groove 12bni by a length"t" (amount of engagement), measured in a radial direction from the rootof the female helicoid 12a to the tip of the engaging projection 17cni,as shown in FIG. 25. The tip of the engaging projection 17cni does notreach the bottom of the linear guide groove 12bni. The length "t" issubstantially the same as the aforementioned length "t'". The engagingprojection 17cni has substantially the same mechanical strength as theengaging projection 17ci. Reference "w" shown in FIG. 25 represents thewidth of the engaging projection 17cni. Reference "x2" shown in FIG. 25designates a corner of the engaging projection 17cni. A line connecting"x2" with "x2" (line x2--x2) is identical to the width of the engagingprojection 17cni "w", which is substantially the same as the width ofthe linear guide groove 12bni. Since the lengths "t" and "t'" aresubstantially the same, the corners "x1", "x1" and "x2" and "x2" aresubstantially located on a common circle (not shown) about the opticalaxis O. In other words, in FIG. 25, the three points, i.e., the corners"x1", "x1" and the optical axis O forms an isosceles triangle, andanother three points, i.e., the corners "x2", "x2" and the optical axisO forms another isosceles triangle. The bases of the two isoscelestriangles each touches a common imaginary circle cc about the opticalaxis O. Due to this arrangement, the bottom surface of each of thelinear guide grooves 12bi, 12bni extends in a plane perpendicular to aradial direction of the cylindrical portion 12p. Another commonimaginary circle (not shown) about the optical axis O, with which thecorners on the bottom of each linear guide groove 12b come in contact,is slightly larger than the common imaginary circle cc, but issubstantially the same as the common imaginary circle cc since the tipof each engaging projection almost touches the bottom of thecorresponding linear guide groove 12b.

The aforementioned other feature of the linear guide mechanism is thatthe part of the outer peripheral surface of the cylindrical portion 12p,which is located at the position opposite to the bottom of the linearguide groove 12bi, can be formed to be a flat surface extending parallelto the bottom surface of the linear guide groove 12bi. This feature willbe hereinafter discussed.

The linear guide barrel 17 does not rotate with respect to the fixedlens barrel block 12. However, since the third moving barrel 16 rotatesrelative to the linear guide barrel 17, the rotational force of thethird moving barrel 16 is transmitted from the male helicoid 16a to thefemale helicoid 12a, and as a result, the linear guide barrel 17 moveslinearly along the optical axis O while receiving that rotational forceat the engaging projections 17c through the linear guide grooves 12b.Therefore, if the aforementioned amount of engagement "t" or "t'" ofeach engaging projection 17c is too short and/or the width "w" or "w'"of each linear guide groove 12b is too narrow, the engaging projections17c may disengage from the respective linear guide grooves 12b when thelinear guide barrel 17 moves linearly along the optical axis O. However,such a problem does not occur if the amount of engagement "t" or "t'" ofeach engaging projection 17c and the width "w" or "w'" of each linearguide groove 12b are designed sufficiently large.

As can be understood from FIG. 27, the larger the width of the linearguide groove 12bi (the length of the line x1--x1) is, the closer eachcorner point x1 comes to the optical axis O. That is, the wider thewidth of the linear guide groove 12bi is, the closer the line x1--x1comes to the optical axis O than the line x2--x2. For this reason, thethickness of the cylindrical portion 12p at the portion thereof wherethe linear guide groove 12bi is formed will become thicker than that atthe portion where the linear guide groove 12bni is formed in the casewhere the bottom of the linear guide groove 12bi is formed so as toalmost touch the tip of the engaging projection 17ci as noted above. Insuch a case, the thickness of the cylindrical portion 12p at the portionthereof where the linear guide groove 12bi is formed will be thickerthan that at the portion where the linear guide groove 12bni is formedby a thickness "y", as shown in FIG. 27. References "L1" and "L2"represent the length from the bottom of the linear guide groove 12bi tothe outer periphery of the cylindrical portion 12p, and the length fromthe bottom of the linear guide groove 12bni to the outer periphery ofthe cylindrical portion 12p, respectively. The thickness "y" is equal tothe difference between lengths "L1" and "L2" (L1-L2=y).

In the present embodiment, as illustrated in FIG. 28, the portion of thecylindrical portion 12p which forms the bottom of the linear guidegroove 12bi is formed to have the same thickness as the portion of thecylindrical portion 12p where the linear guide groove 12bni is formed,by cutting off part of an outer layer of the cylindrical portion 12p byan amount corresponding to the thickness "y". By so doing, the part ofthe outer peripheral surface of the cylindrical portion 12p, which islocated at the position opposite to the bottom of the linear guidegroove 12bi, is formed to be a flat surface 12x extending parallel tothe bottom surface of the linear guide groove 12bi.

The flat surface 12x is located immediately next to a flat surface PT1of a wall PT forming a film chamber FC of the zoom lens camera of thepresent embodiment. The wall PT is secured to the fixed lens barrelblock 12, and the flat surface PT1 extends parallel to the flat surface12x. Since the flat surface 12x is formed by cutting off part of anouter layer of the cylindrical portion 12p in such a manner as notedabove, the film chamber FC is successfully located closer to thecylindrical portion 12p towards the optical axis O, by the amountcorresponding to the aforementioned thickness "y", which contributes tothe minimization of the size of the zoom lens camera of the presentembodiment, particularly, in the width of the camera. This effectivestructure to minimize the width of the zoom lens camera can beappreciated by comparing a distance "H" from the optical axis O to theflat surface 12x with a distance "R" from the optical axis O to an outerperipheral surface of the cylindrical portion 12p on which the flatsurface 12x is not formed, as shown in FIG. 29. The distances "H" and"R" are also illustrated in FIG. 25. The front and rear of the zoom lenscamera of the present embodiment respectively correspond to the up anddown as viewed in FIG. 29.

In the zoom lens camera of the present embodiment, the aforementionedanother feature of the linear guide mechanism is adopted to the linearguide groove 12bi and the engaging projection 17ci. However, such afeature may be applied to any other linear guiding groove and engagingprojection which engage with each other.

In the above-described embodiment of the zoom lens barrel 10, althoughthe zoom lens optical system consists of two movable lens groups, namelythe front lens group L1 and the rear lens group L2, it should beunderstood that the present invention is not limited to the presentembodiment disclosed above, but the present invention may also beapplied to another type of zoom lens optical system including one ormore fixed lens group.

In addition, in the above embodiment, the rear lens group L1 is providedas a component of the AF/AE shutter unit 21, and the AE motor 29 and therear lens group driving motor 30 are mounted to the AF/AE shutter unit21. With such a structure, the structure for supporting the front andrear lens groups L1 and L2 and the structure for driving the rear lensgroup L2 are both simplified. Instead of adopting such a structure, thezoom lens barrel 10 may also be realized in such a manner by making therear lens group L2 a member separate from the AF/AE shutter unit 21,which is provided with the shutter mounting stage 40, the circulardriving member 49, the supporting member 47, the shutter blades 27, theshutter blade supporting ring 46 and the like, and that the rear lensgroup L2 is supported by any supporting member other than the AF/AEshutter unit 21.

In the zoom lens camera of the present embodiment, the operation byrotation of the whole optical unit driving motor 25 and the rear lensgroup driving motor 30 will now be described with reference to FIGS. 17,18, 19 and 20.

As shown in FIGS. 18 or 20, when the zoom lens barrel 10 is at the mostretracted (withdrawn) position, i.e., the lens-housed condition, whenthe power switch is turned ON, the whole optical unit driving motor 25is driven to rotate its drive shaft in the forward rotational directionby a small amount. This rotation of the motor 25 is transmitted to thedriving pinion 15 through the gear train 26, which is supported by thesupporting member 32 formed integral with the fixed lens barrel block12, to thereby rotate the third moving barrel 16 in one predeterminedrotational direction to advance forwardly along the optical axis O.Therefore, the second moving barrel 19 and the first moving barrel 20are each advanced by a small amount in the optical axis direction, alongwith the third moving barrel 16. Consequently, the camera is in a statecapable of photographing, with the zoom lens positioned at the widestposition, i.e., the wide end. At this stage, due to the fact that theamount of movement of the linear guide barrel 17, with respect to thefixed lens barrel block 12, is detected through the relative slidebetween the code plate 13a and the contacting terminal 9, the focallength of the zoom lens barrel 10, i.e., the front and rear lens groupsL1 and L2, is detected.

In the photographable state as above described, when the aforementionedzoom operating lever is manually moved towards a "tele" side, or the"tele" zoom button is manually depressed to be turned ON, the wholeoptical unit driving motor 25 is driven to rotate its drive shaft in theforward rotational direction through the whole optical unit drivingmotor controller 60 so that the third moving barrel 16 rotates in therotational direction to advance along the optical axis O via the drivingpinion 15 and the outer peripheral gear 16b. Therefore, the third movingbarrel 16 is advanced from the fixed lens barrel block 12 according tothe relationship between the female helicoid 12a and the male helicoid16a. At the same time, the linear guide barrel 17 moves forwardly in theoptical axis direction together with the third moving barrel 16, withoutrelative rotation to the fixed lens barrel block 12, according to therelationship between the engaging projections 17c and the linear guidegrooves 12b. At this time, the simultaneous engagement of the followerpins 18 with the respective lead slots 17b and linear guide grooves 16ccauses the second moving barrel 19 to move forwardly relative to thethird moving barrel 16 in the optical axis direction, while rotatingtogether with the third moving barrel 16 in the same rotationaldirection relative to the fixed lens barrel block 12. The first movingbarrel 20 moves forwardly from the second moving barrel 19 in theoptical axis direction, together with the AF/AE shutter unit 21, withoutrelative rotation to the fixed lens barrel block 12, due to theabove-noted structures in which the first moving barrel 20 is guidedlinearly by the linear guide member 22 and in which the follower pins 24are guided by the lead grooves 19c. During such movements, according tothe fact that the moving position of the linear guide barrel 17 withrespect to the fixed lens barrel block 12 is detected through therelative slide between the code plate 13a and the contacting terminal 9,the focal length set by the zoom operation device 62 is detected.

Conversely, when the zoom operating lever is manually moved towards a"wide" side, or the "wide" zoom button is manually depressed to beturned ON, the whole optical unit driving motor 25 is driven to rotateits drive shaft in the reverse rotational direction through the wholeoptical unit driving motor controller 60 so that the third moving barrel16 rotates in the rotational direction to retract into the fixed lensbarrel block 12 together with the linear guide barrel 17. At the sametime, the second moving barrel 19 is retracted into the third movingbarrel 16, while rotating in the same direction as that of the thirdmoving barrel 16, and the first moving barrel 20 is retracted into therotating second moving barrel 19 together with the AF/AE shutter unit21. During the above retraction driving, like the case of advancingdriving as above described, the rear lens group driving motor 30 is notdriven.

While the zoom lens barrel 10 is driven during the zooming operation,since the rear lens group driving motor 30 is not driven, the front lensgroup L1 and the rear lens group L2 move as a whole, maintaining aconstant distance between each other, as shown in FIGS. 17 or 19. Thefocal length input via the zoom code plate 13a and the contactingterminal 9 is indicated on an LCD panel (not shown) provided on thecamera body.

At any focal length set by the zoom operating device 62, when therelease button is depressed by a half-step, the object distancemeasuring apparatus 64 is actuated to measure a current subjectdistance. At the same time the photometering apparatus 65 is actuated tomeasure a current subject brightness. Thereafter, when the releasebutton is fully depressed, the whole optical unit driving motor 25 andthe rear lens group driving motor 30 are each driven by respectiveamounts dictated according to the focal length information set inadvance and the subject distance information obtained from the objectdistance measuring apparatus 64, so that the front and rear lens groupsL1 and L2 are respectively moved to specified positions to obtain aspecified focal length to thereby bring the subject into focus.Immediately after the subject is brought into focus, via the AE motorcontroller 66, the AE motor 29 is driven to rotate the circular drivingmember 49 by an amount corresponding to the subject brightnessinformation obtained from the photometering apparatus 65 so that theshutter 27 is driven to open the shutter blades 27a by a specifiedamount which satisfies the required exposure. Immediately after such ashutter release operation, in which the three shutter blades 27a areopened and subsequently closed, is completed, the whole optical unitdriving motor 25 and the rear lens group driving motor 30 are bothdriven to move the front lens group L1 and the rear lens group L2 to therespective initial positions at which they were at prior to a shutterrelease.

In the present embodiment of the zoom lens barrel 10, "Fantas Coat SF-6"is used as the coating 72e. However, a different type of coating may beused as the coating 72e as long as it is waterproof and makes thecircular abutting surface 72b a smooth surface to form substantially nogap between the circular abutting surface 72b and the circumferentialportion fp.

Obvious changes may be made in the specific embodiments of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

What is claimed is:
 1. A lens barrel comprising:an outer barrel, aninner periphery of said outer barrel being provided with a first threadand at least one linear guide groove intersecting said first thread,said at least one linear guide groove extending in a direction of anoptical axis of said lens barrel; a middle barrel an outer periphery ofsaid middle barrel being, provided with a second thread meshing withsaid first thread; an inner barrel positioned inside said middle barrel,said inner barrel being provided with at least one follower whichengages with said at least one linear guide groove, so that said innerbarrel is guided along said optical axis without rotating about saidoptical axis with respect to said outer barrel; and a recess formed at afront end of each of said at least one linear guide groove on said innerperiphery of said outer barrel, said recess having a width dimensionwhich provides for rotational movement of said at least one followerinto said at least one linear guide groove during initial meshing ofsaid middle barrel with said outer barrel.
 2. The lens barrel accordingto claim 1, further comprising an annular retaining member which engageswith a front end of said outer barrel after said middle barrel hasengaged with said outer barrel.
 3. The lens barrel according to claim 2,wherein said annular retaining member comprises at least one engagingprojection which engages with said at least one recess.
 4. The lensbarrel according to claim 3, wherein said at least one engagingprojection comprises a surface, said surface determining a frontextremity of said at least one linear guide groove.
 5. The lens barrelaccording to claim 3, wherein said at least one linear guide groove isdefined between a first side surface and a second side surface of saidinner periphery of said outer barrel, said first and said second sidesurfaces extending in said direction of said optical axis, and whereinsaid at least one engaging projection comprises a linear guide surfacewhich linearly guides said at least one follower, together with saidfirst side surface.
 6. The lens barrel according to claim 5, wherein adistance between said first side surface and said second side surface isless than a distance between said linear guide surface and said secondside surface.
 7. The lens barrel according to claim 1, wherein a surfaceof said recess is inclined in a plane parallel to said first thread. 8.The lens barrel according to claim 1, wherein said outer barrel isintegrally formed with a stationary block provided inside a camera body.9. The lens barrel according to claim 1, wherein said middle barrel ismovable along said optical axis together with said inner barrel suchthat a distance between said middle barrel and said inner barrel remainsconstant while said middle barrel rotates about said optical axisrelative to said inner barrel.
 10. The lens barrel according to claim 1,wherein said at least one follower is formed at a rear end of said innerbarrel, said at least one follower projecting outwardly in a radialdirection of said inner barrel to engage with said at least one linearguide groove.
 11. The lens barrel according to claim 3, wherein said atleast one engaging projection comprises an engaging claw which projectsoutwardly in a radial direction of said annular retaining member, saidengaging claw engaging with a hole formed in said recess.
 12. The lensbarrel according to claim 1, further comprising at least one projectionformed at a bottom of said at least one linear guide groove, said atleast one projection engaging with said second thread so as to functionas a part of said first thread.
 13. The lens barrel according to claim1, wherein said at least one follower and said at least one linear guidegroove each have a width greater that a predetermined minimum width anda height equal to a predetermined minimum height, said predeterminedminimum width and said predetermined minimum height being determined toprovide for rotational movement of said at least one follower into saidat least one linear guide groove.
 14. The lens barrel according to claim12, wherein said at least one projection is formed substantially in amiddle of said at least one linear guide groove in a circumferentialdirection of said outer barrel.
 15. A lens barrel comprising:an outerbarrel, an inner periphery of said outer barrel being provided with afirst thread and a plurality of linear guide grooves each intersectingsaid first thread, said plurality of linear guide grooves extending in adirection of an optical axis of said lens barrel; a middle barrel, anouter periphery of said middle barrel being provided with a secondthread meshing with said first thread so that said middle barrel ismovable along said optical axis while rotating about said optical axiswith respect to said outer barrel; an inner barrel positioned insidesaid middle barrel and moved together with said inner barrel along saidoptical axis, a rear end of said inner barrel including a plurality offollowers which respectively engage with said plurality of linear guidegrooves so that inner barrel is guided along said optical axis withoutrotating about said optical axis with respect to said outer barrel; aplurality of recesses each formed at a front end of a corresponding oneof said plurality of linear guide grooves on said inner periphery ofsaid outer barrel, said plurality of recesses each having a widthgreater than said corresponding one of said plurality of linear guidegrooves; and an annular retaining member for preventing said middlebarrel from disengaging from said outer barrel, said annular retainingmember being provided with a plurality of engaging projections eachextending in said direction of said optical axis to engage with acorresponding one of said plurality of recesses, said annular retainingmember being secured to a front end of said outer barrel after saidmiddle barrel has been engaged with said outer barrel and said pluralityof engaging projections have respectively engaged with said plurality oflinear guide grooves.
 16. A lens barrel comprising:an outer barrelprovided on an inner periphery with a first thread; a middle barrelprovided on an outer periphery with a second thread meshing with saidfirst thread of said outer barrel; an inner barrel positioned insidesaid middle barrel and provided with at least one follower; an annularretaining member secured to a front end of said outer barrel whichprevents said middle barrel from disengaging from said outer barrel; atleast one linear guide groove which extends in a direction of an opticalaxis of said lens barrel and with which said at least one followerengages, wherein a portion of said at least one linear guide groove isformed on said annular retaining member and a remaining portion of saidat least one linear guide groove is formed on an inner periphery of saidouter barrel.
 17. A lens barrel comprising:an outer barrel provided onan inner periphery with a first thread and a linear guide grooveintersecting said first thread and extending in a direction of anoptical axis of said lens barrel; a middle barrel provided on an outerperiphery with a second thread meshing with said first thread; an innerbarrel positioned inside said middle barrel and provided with a followerwhich engages with said linear guide groove to be guided along saidlinear guide groove, said middle barrel being movable along said opticalaxis together with said inner barrel such that a distance between saidmiddle and said inner barrels remains constant while said middle barrelrotates about said optical axis relative to said inner barrel; and atleast one projection formed at a bottom of said linear guide groove,said at least one projection engaging with said second thread so as tofunction as a part of said first thread.